Sustained released of bioactive mesenchymal stromal cell-derived extracellular vesicles from 3D-printed gelatin methacrylate hydrogels

Mesenchymal stem cell-secretome laden photopolymerizable hydrogels for wound healing

Mesenchymal stem cell-derived secretome represents an emerging acellular therapeutic which possess significant opportunity for clinical applications due to its anti-inflammatory, immunomodulatory, and wound healing properties. However, maintaining therapeutic efficacy and ensuring stability of cell-based products is challenging, requiring a robust delivery method. Therefore, we designed a hydrogel-based scaffold loaded with CK Cell Technologies' proprietary Mesenchymal stem cell-secretome for controlled release treatment of acute and chronic wounds. We incorporated both conditioned media (CM) and extracellular vesicles (EVs) into gelatin methacryloyl (GelMA) hydrogels and demonstrated how we can tune the diffusive release of the EVs from them. To demonstrate viability of the approach, we developed a wound healing scratch assay where we see in situ release of CM and EVs promote enhanced migration of human dermal fibroblasts (hDFs). We see the colocalization of these EVs in the fibroblasts using fluorescent microscopy. Finally, as a surrogate for in vivo neovascularization, we conducted an in vitro tube formation assay for the MSC-secretome using matrigel-embedded human microvascular endothelial cells. By adding CM and EVs, we observe an increase in tubulogenesis. Collectively, our data demonstrates by tuning the GelMA properties, we can influence the controlled release of the MSC-secretome for a wound dressing and bandage application for chronic and acute wounds.

Bioactive poly(salicylic acid)-poly(citric acid) scaffolds improve diabetic wound repair via regulating HIF-1α, Nrf2 and macrophage

Diabetic wounds environment is over-oxidized, over-inflammatory, leading to difficulties in regenerating blood vessels, and retardation of healing in diabetic wounds. Therefore, diabetic wounds can be treated from the perspective of scavenging oxidative free radicals and reducing the level of inflammation. Herein, we report a bioactive poly(salicylic acid)-poly(citric acid) (FPSa-PCG) hydrogel for diabetic wound repair. The FPSa-PCG hydrogel shows abilities of antioxidation, anti-inflammation, and regulation of macrophage phenotype. The FPSa-PCG hydrogel showed good biocompatibility, and obtain the abilities of promotion of macrophages migration, reduction of ROS generation, suppression of the M1-type macrophage polarization. FPSa and PCG could synergistically enhance the angiogenesis through upregulating the mRNA expression of HIF1Α, VEGF, and CD31 in endothelial cells and reduce the ROS level of macrophages through upregulating the mRNA expression of Nrf2. The in vivo diabetic wound model confirmed the promoting effect of FPSa-PCG hydrogel on wound closure in diabetes. The further studies found that FPSa-PCG hydrogel could induce the CD31 protein expression in the subcutaneous tissue and inhibit the TNF-a protein expression. This work shows that the simple composition FPSa-PCG hydrogel has a promising therapeutic potential in the treatment of diabetic wounds.

Unveiling the versatility of gelatin methacryloyl hydrogels: a comprehensive journey into biomedical applications

Gelatin methacryloyl (GelMA) hydrogels have gained significant recognition as versatile biomaterials in the biomedical domain. GelMA hydrogels emulate vital characteristics of the innate extracellular matrix by integrating cell-adhering and matrix metalloproteinase-responsive peptide motifs. These features enable cellular proliferation and spreading within GelMA-based hydrogel scaffolds. Moreover, GelMA displays flexibility in processing, as it experiences crosslinking when exposed to light irradiation, supporting the development of hydrogels with adjustable mechanical characteristics. The drug delivery landscape has been reshaped by GelMA hydrogels, offering a favorable platform for the controlled and sustained release of therapeutic actives. The tunable physicochemical characteristics of GelMA enable precise modulation of the kinetics of drug release, ensuring optimal therapeutic effectiveness. In tissue engineering, GelMA hydrogels perform an essential role in the design of the scaffold, providing a biomimetic environment conducive to cell adhesion, proliferation, and differentiation. Incorporating GelMA in three-dimensional printing further improves its applicability in drug delivery and developing complicated tissue constructs with spatial precision. Wound healing applications showcase GelMA hydrogels as bioactive dressings, fostering a conducive microenvironment for tissue regeneration. The inherent biocompatibility and tunable mechanical characteristics of GelMA provide its efficiency in the closure of wounds and tissue repair. GelMA hydrogels stand at the forefront of biomedical innovation, offering a versatile platform for addressing diverse challenges in drug delivery, tissue engineering, and wound healing. This review provides a comprehensive overview, fostering an in-depth understanding of GelMA hydrogel's potential impact on progressing biomedical sciences.

3D bioprinting approaches for spinal cord injury repair

Regenerative healing of spinal cord injury (SCI) poses an ongoing medical challenge by causing persistent neurological impairment and a significant socioeconomic burden. The complexity of spinal cord tissue presents hurdles to successful regeneration following injury, due to the difficulty of forming a biomimetic structure that faithfully replicates native tissue using conventional tissue engineering scaffolds. 3D bioprinting is a rapidly evolving technology with unmatched potential to create 3D biological tissues with complicated and hierarchical structure and composition. With the addition of biological additives such as cells and biomolecules, 3D bioprinting can fabricate preclinical implants, tissue or organ-like constructs, andin vitromodels through precise control over the deposition of biomaterials and other building blocks. This review highlights the characteristics and advantages of 3D bioprinting for scaffold fabrication to enable SCI repair, including bottom-up manufacturing, mechanical customization, and spatial heterogeneity. This review also critically discusses the impact of various fabrication parameters on the efficacy of spinal cord repair using 3D bioprinted scaffolds, including the choice of printing method, scaffold shape, biomaterials, and biological supplements such as cells and growth factors. High-quality preclinical studies are required to accelerate the translation of 3D bioprinting into clinical practice for spinal cord repair. Meanwhile, other technological advances will continue to improve the regenerative capability of bioprinted scaffolds, such as the incorporation of nanoscale biological particles and the development of 4D printing.

3D bioprinted small extracellular vesicles from periodontal cells enhance mesenchymal stromal cell function

Recent research indicates that combining 3D bioprinting and small extracellular vesicles (sEVs) offers a promising 'cell-free' regenerative medicine approach for various tissue engineering applications. Nonetheless, the majority of existing research has focused on bioprinting of sEVs sourced from cell lines. There remains a notable gap in research regarding the bioprinting of sEVs derived from primary human periodontal cells and their potential impact on ligamentous and osteogenic differentiation. Here, we investigated the effect of 3D bioprinted periodontal cell sEVs constructs on the differentiation potential of human buccal fat pad-derived mesenchymal stromal cells (hBFP-MSCs). Periodontal cell-derived sEVs were enriched by size exclusion chromatography (SEC) with particle-shaped morphology, and characterized by being smaller than 200 nm in size and CD9/CD63/CD81 positive, from primary human periodontal ligament cells (hPDLCs) and human gingival fibroblasts (hGFs). The sEVs were then 3D bioprinted in 10 % gelatin methacryloyl (GelMA) via microextrusion bioprinting. Release of sEVs from bioprinted constructs was determined by DiO-labelling and confocal imaging, and CD9 ELISA. Attachment and ligament/osteogenic/cementogenic differentiation of hBFP-MSCs was assessed on bioprinted GelMA, without and with sEVs (GelMA/hPDLCs-sEVs and GelMA/hGFs-sEVs), scaffolds. hBFP-MSCs seeded on the bioprinted sEVs constructs spread well with significantly enhanced focal adhesion, mechanotransduction associated gene expression, and ligament and osteogenesis/cementogenesis differentiation markers in GelMA/hPDLCs-sEVs, compared to GelMA/hGFs-sEVs and GelMA groups. A 2-week osteogenic and ligamentous differentiation showed enhanced ALP staining, calcium formation and toluidine blue stained cells in hBFP-MSCs on bioprinted GelMA/hPDLCs-sEVs constructs compared to the other two groups. The proof-of-concept data from this study supports the notion that 3D bioprinted GelMA/hPDLCs-sEVs scaffolds promote cell attachment, as well as ligamentous, osteogenic and cementogenic differentiation, of hBFP-MSCs in vitro.

Hydrogel-mediated extracellular vesicles for enhanced wound healing: the latest progress, and their prospects for 3D bioprinting

Extracellular vesicles have shown promising tissue recovery-promoting effects, making them increasingly sought-after for their therapeutic potential in wound treatment. However, traditional extracellular vesicle applications suffer from limitations such as rapid degradation and short maintenance during wound administration. To address these challenges, a growing body of research highlights the role of hydrogels as effective carriers for sustained extracellular vesicle release, thereby facilitating wound healing. The combination of extracellular vesicles with hydrogels and the development of 3D bioprinting create composite hydrogel systems boasting excellent mechanical properties and biological activity, presenting a novel approach to wound healing and skin dressing. This comprehensive review explores the remarkable mechanical properties of hydrogels, specifically suited for loading extracellular vesicles. We delve into the diverse sources of extracellular vesicles and hydrogels, analyzing their integration within composite hydrogel formulations for wound treatment. Different composite methods as well as 3D bioprinting, adapted to varying conditions and construction strategies, are examined for their roles in promoting wound healing. The results highlight the potential of extracellular vesicle-laden hydrogels as advanced therapeutic tools in the field of wound treatment, offering both mechanical support and bioactive functions. By providing an in-depth examination of the various roles that these composite hydrogels can play in wound healing, this review sheds light on the promising directions for further research and development. Finally, we address the challenges associated with the application of composite hydrogels, along with emerging trends of 3D bioprinting in this domain. The discussion covers issues such as scalability, regulatory considerations, and the translation of this technology into practical clinical settings. In conclusion, this review underlines the significant contributions of hydrogel-mediated extracellular vesicle therapy to the field of 3D bioprinting and wound healing and tissue regeneration. It serves as a valuable resource for researchers and practitioners alike, fostering a deeper understanding of the potential benefits, applications, and challenges involved in utilizing composite hydrogels for wound treatment.

Unraveling the Multifaceted Roles of Extracellular Vesicles: Insights into Biology, Pharmacology, and Pharmaceutical Applications for Drug Delivery

Extracellular vesicles (EVs) are nanoparticles released from various cell types that have emerged as powerful new therapeutic option for a variety of diseases. EVs are involved in the transmission of biological signals between cells and in the regulation of a variety of biological processes, highlighting them as potential novel targets/platforms for therapeutics intervention and/or delivery. Therefore, it is necessary to investigate new aspects of EVs' biogenesis, biodistribution, metabolism, and excretion as well as safety/compatibility of both unmodified and engineered EVs upon administration in different pharmaceutical dosage forms and delivery systems. In this review, we summarize the current knowledge of essential physiological and pathological roles of EVs in different organs and organ systems. We provide an overview regarding application of EVs as therapeutic targets, therapeutics, and drug delivery platforms. We also explore various approaches implemented over the years to improve the dosage of specific EV products for different administration routes.

Extracellular vesicle biopotentiated hydrogels for diabetic wound healing: The art of living nanomaterials combined with soft scaffolds

Diabetic wounds (DWs) pose a major challenge for the public health system owing to their high incidence, complex pathogenesis, and long recovery time; thus, there is an urgent need to develop innovative therapies to accelerate the healing process of diabetic wounds. As natural nanovesicles, extracellular vesicles (EVs) are rich in sources with low immunogenicity and abundant nutritive molecules and exert potent therapeutic effects on diabetic wound healing. To avoid the rapid removal of EVs, a suitable delivery system is required for their controlled release. Owing to the advantages of high porosity, good biocompatibility, and adjustable physical and chemical properties of hydrogels, EV biopotentiated hydrogels can aid in achieving precise and favorable therapy against diabetic wounds. This review highlights the different design strategies, therapeutic effects, and mechanisms of EV biopotentiated hydrogels. We also discussed the future challenges and opportunities of using EV biopotentiated hydrogels for diabetic wound healing.

Microfiber-reinforced hydrogels prolong the release of human induced pluripotent stem cell-derived extracellular vesicles to promote endothelial migration

Extracellular vesicle (EV)-based approaches for promoting angiogenesis have shown promising results. Yet, further development is needed in vehicles that prolong EV exposure to target organs. Here, we hypothesized that microfiber-reinforced gelatin methacryloyl (GelMA) hydrogels could serve as sustained delivery platforms for human induced pluripotent stem cell (hiPSC)-derived EV. EV with 50-200 nm size and typical morphology were isolated from hiPSC-conditioned culture media and tested negative for common co-isolated contaminants. hiPSC-EV were then incorporated into GelMA hydrogels with or without a melt electrowritten reinforcing mesh. EV release was found to increase with GelMA concentration, as 12 % (w/v) GelMA hydrogels provided higher release rate and total release over 14 days in vitro, compared to lower hydrogel concentrations. Release profile modelling identified diffusion as a predominant release mechanism based on a Peppas-Sahlin model. To study the effect of reinforcement-dependent hydrogel mechanics on EV release, stress relaxation was assessed. Reinforcement with highly porous microfiber meshes delayed EV release by prolonging hydrogel stress relaxation and reducing the swelling ratio, thus decreasing the initial burst and overall extent of release. After release from photocrosslinked reinforced hydrogels, EV remained internalizable by human umbilical vein endothelial cells (HUVEC) over 14 days, and increased migration was observed in the first 4 h. EV and RNA cargo stability was investigated at physiological temperature in vitro, showing a sharp decrease in total RNA levels, but a stable level of endothelial migration-associated small noncoding RNAs over 14 days. Our data show that hydrogel formulation and microfiber reinforcement are superimposable approaches to modulate EV release from hydrogels, thus depicting fiber-reinforced GelMA hydrogels as tunable hiPSC-EV vehicles for controlled release systems that promote endothelial cell migration.

The role of microfluidics and 3D-bioprinting in the future of exosome therapy

Exosome-based strategies constitute a promising tool for therapeutics, avoiding potential immunogenic and tumorigenic side-effects of cell therapies. However, the collection of a suitable exosome pool, and the need for high doses with conventional administration approaches, hamper their clinical translation. To overcome these challenges, versatile exosome collection strategies together with advanced delivery platforms may represent major progress in this field. Microfluidics enables large-scale gathering of both natural and synthetic exosomes for their implementation into bioinks, while 3D-bioprinting holds great promise in regenerative medicine with the use of exosome-loaded scaffolds that mimic the target tissue with controlled pharmacokinetics and pharmacodynamics. Hence, the combination of both strategies might become the key for the translation of exosome therapies to clinical practice.

Exosomes from umbilical cord-derived mesenchymal stem cells combined with gelatin methacryloyl inhibit vein graft restenosis by enhancing endothelial functions

BACKGROUND

The prevalence of coronary artery disease is increasing. As a common treatment method, coronary artery bypass transplantation surgery can improve heart problems while also causing corresponding complications. Venous graft restenosis is one of the most critical and intractable complications. Stem cell-derived exosomes could have therapeutic promise and value. However, as exosomes alone are prone to inactivation and easy removal, this therapeutic method has not been widely used in clinical practice. Methacrylated gelatin (GelMA) is a polymer with a loose porous structure that maintains the biological activity of the exosome and can control its slow release in vivo. In this study, we combined human umbilical cord mesenchymal stem cell-derived exosomes (hUCMSC-Exos) and GelMA to explore their effects and underlying mechanisms in inhibiting venous graft restenosis.

RESULTS

Human umbilical cord mesenchymal stem cells (hUCMSCs) were appraised using flow cytometry. hUCMSC-Exos were evaluated via transmission electron microscopy and western blotting. hUCMSC-Exos embedded in a photosensitive GelMA hydrogel (GelMA-Exos) were applied topically around venous grafts in a rat model of cervical arteriovenous transplantation, and their effects on graft reendothelialization and restenosis were evaluated through ultrasonic, histological, and immunofluorescence examinations. Additionally, we analyzed the material properties, cellular reactions, and biocompatibility of the hydrogels. We further demonstrated that the topical application of GelMA-Exos could accelerate reendothelialization after autologous vein transplantation and reduce restenosis in the rat model. Notably, GelMA-Exos caused neither damage to major organs in mice nor excessive immune rejection. The uptake of GelMA-Exos by endothelial cells stimulated cell proliferation and migration in vitro. A bioinformatic analysis of existing databases revealed that various cell proliferation and apoptosis pathways, including the mammalian target of rapamycin (mTOR)-phosphoinositide 3-kinase (PI3K)-AKT signaling pathways, might participate in the underlying regulatory mechanism.

CONCLUSIONS

Compared with the tail vein injection of hUCMSC-Exos, the local application of a mixture of hUCMSC-Exos and GelMA was more effective in promoting endothelial repair of the vein graft and inhibiting restenosis. Therefore, the proposed biomaterial-based therapeutic approach is a promising treatment for venous graft restenosis.

Exosome-bearing hydrogels and cardiac tissue regeneration

BACKGROUND

In recent years, cardiovascular disease in particular myocardial infarction (MI) has become the predominant cause of human disability and mortality in the clinical setting. The restricted capacity of adult cardiomyocytes to proliferate and restore the function of infarcted sites is a challenging issue after the occurrence of MI. The application of stem cells and byproducts such as exosomes (Exos) has paved the way for the alleviation of cardiac tissue injury along with conventional medications in clinics. However, the short lifespan and activation of alloreactive immune cells in response to Exos and stem cells are the main issues in patients with MI. Therefore, there is an urgent demand to develop therapeutic approaches with minimum invasion for the restoration of cardiac function.

MAIN BODY

Here, we focused on recent data associated with the application of Exo-loaded hydrogels in ischemic cardiac tissue. Whether and how the advances in tissue engineering modalities have increased the efficiency of whole-based and byproducts (Exos) therapies under ischemic conditions. The integration of nanotechnology and nanobiology for designing novel smart biomaterials with therapeutic outcomes was highlighted.

CONCLUSION

Hydrogels can provide suitable platforms for the transfer of Exos, small molecules, drugs, and other bioactive factors for direct injection into the damaged myocardium. Future studies should focus on the improvement of physicochemical properties of Exo-bearing hydrogel to translate for the standard treatment options.

3D Printing of Microenvironment-Specific Bioinspired and Exosome-Reinforced Hydrogel Scaffolds for Efficient Cartilage and Subchondral Bone Regeneration

In clinical practice, repairing osteochondral defects presents a challenge due to the varying biological properties of articular cartilages and subchondral bones. Thus, elucidating how spatial microenvironment-specific biomimetic scaffolds can be used to simultaneously regenerate osteochondral tissue is an important research topic. Herein, a novel bioinspired double-network hydrogel scaffold produced via 3D printing with tissue-specific decellularized extracellular matrix (dECM) and human adipose mesenchymal stem cell (MSC)-derived exosomes is described. The bionic hydrogel scaffolds promote rat bone marrow MSC attachment, spread, migration, proliferation, and chondrogenic and osteogenic differentiation in vitro, as determined based on the sustained release of bioactive exosomes. Furthermore, the 3D-printed microenvironment-specific heterogeneous bilayer scaffolds efficiently accelerate the simultaneous regeneration of cartilage and subchondral bone tissues in a rat preclinical model. In conclusion, 3D dECM-based microenvironment-specific biomimetics encapsulated with bioactive exosomes can serve as a novel cell-free recipe for stem cell therapy when treating injured or degenerative joints. This strategy provides a promising platform for complex zonal tissue regeneration whilst holding attractive clinical translation potential.

Mesenchymal stem cell-derived extracellular vesicles in skin wound healing: roles, opportunities and challenges

Skin wounds are characterized by injury to the skin due to trauma, tearing, cuts, or contusions. As such injuries are common to all human groups, they may at times represent a serious socioeconomic burden. Currently, increasing numbers of studies have focused on the role of mesenchymal stem cell (MSC)-derived extracellular vesicles (EVs) in skin wound repair. As a cell-free therapy, MSC-derived EVs have shown significant application potential in the field of wound repair as a more stable and safer option than conventional cell therapy. Treatment based on MSC-derived EVs can significantly promote the repair of damaged substructures, including the regeneration of vessels, nerves, and hair follicles. In addition, MSC-derived EVs can inhibit scar formation by affecting angiogenesis-related and antifibrotic pathways in promoting macrophage polarization, wound angiogenesis, cell proliferation, and cell migration, and by inhibiting excessive extracellular matrix production. Additionally, these structures can serve as a scaffold for components used in wound repair, and they can be developed into bioengineered EVs to support trauma repair. Through the formulation of standardized culture, isolation, purification, and drug delivery strategies, exploration of the detailed mechanism of EVs will allow them to be used as clinical treatments for wound repair. In conclusion, MSC-derived EVs-based therapies have important application prospects in wound repair. Here we provide a comprehensive overview of their current status, application potential, and associated drawbacks.

Engineered extracellular vesicles as therapeutics of degenerative orthopedic diseases

Degenerative orthopedic diseases, as a global public health problem, have made serious negative impact on patients' quality of life and socio-economic burden. Traditional treatments, including chemical drugs and surgical treatments, have obvious side effects and unsatisfactory efficacy. Therefore, biological therapy has become the focus of researches on degenerative orthopedic diseases. Extracellular vesicles (EVs), with superior properties of immunoregulatory, growth support, and drug delivery capabilities, have emerged as a new cell-free strategy for the treatment of many diseases, including degenerative orthopedic diseases. An increasing number of studies have shown that EVs can be engineered through cargo loading, surface modification, and chemical synthesis to improve efficiency, specificity, and safety. Herein, a comprehensive overview of recent advances in engineering strategies and applications of engineered EVs as well as related researches in degenerative orthopedic diseases, including osteoarthritis (OA), osteoporosis (OP), intervertebral disc degeneration (IDD) and osteonecrosis of the femoral head (ONFH), is provided. In addition, we analyze the potential and challenges of applying engineered EVs to clinical practice.

Extracellular vesicles: a comprehensive review of their roles as biomarkers and potential therapeutics in psoriasis and psoriatic arthritis

Psoriasis is a chronic immune-mediated condition that affects the skin and joints, with current treatments still unable to offer a cure and long-term use of treatments posing health risks. Understanding the pathogenesis of the disease has helped identify new targets that have allowed for the expansion of the therapeutic arsenal. Extracellular vesicles (EVs) have recently emerged as pathophysiological mediators of psoriasis, and there have been increasing reports of EVs as potential biomarkers and therapeutics. Given their innate role as natural vehicles for cell-to-cell communication, EVs have vast potential in their ability to determine disease status based on EV-specific cargo as well as act as therapeutics because of their anti-inflammatory properties and potential for enhancement. In this review we summarize the role of EVs in the pathogenesis of psoriasis and discuss EVs as both diagnostic and therapeutic agents.

Production and Utility of Extracellular Vesicles with 3D Culture Methods

In recent years, extracellular vesicles (EVs) have emerged as promising biomarkers, cell-free therapeutic agents, and drug delivery carriers. Despite their great clinical potential, poor yield and unscalable production of EVs remain significant challenges. When using 3D culture methods, such as scaffolds and bioreactors, large numbers of cells can be expanded and the cell environment can be manipulated to control the cell phenotype. This has been employed to successfully increase the production of EVs as well as to enhance their therapeutic effects. The physiological relevance of 3D cultures, such as spheroids, has also provided a strategy for understanding the role of EVs in the pathogenesis of several diseases and to evaluate their role as tools to deliver drugs. Additionally, 3D culture methods can encapsulate EVs to achieve more sustained therapeutic effects as well as prevent premature clearance of EVs to enable more localised delivery and concentrated exosome dosage. This review highlights the opportunities and drawbacks of different 3D culture methods and their use in EV research.

Optimization of methacrylated gelatin /layered double hydroxides nanocomposite cell-laden hydrogel bioinks with high printability for 3D extrusion bioprinting

Layered double hydroxides (LDHs) offer unique source of inspiration for design of bone mimetic biomaterials due to their superior mechanical properties, drug delivery capability and regulation cellular behaviors, particularly by divalent metal cations in their structure. Three-dimensional (3D) bioprinting of LDHs holds great promise as a novel strategy thanks to highly tunable physiochemical properties and shear-thinning ability of LDHs, which allow shape fidelity after deposition. Herein, we introduce a straightforward strategy for extrusion bioprinting of cell laden nanocomposite hydrogel bioink of gelatin methacryloyl (GelMA) biopolymer and LDHs nanoparticles. First, we synthesized LDHs by co-precipitation process and systematically examined the effect of LDHs addition on printing parameters such as printing pressure, extrusion rate, printing speed, and finally bioink printability in creating grid-like constructs. The developed hydrogel bioinks provided precise control over extrudability, extrusion uniformity, and structural integrity after deposition. Based on the printability and rheological analysis, the printability could be altered by controlling the concentration of LDHs, and printability was found to be ideal with the addition of 3 wt % LDHs. The addition of LDHs resulted in remarkably enhanced compressive strength from 652 kPa (G-LDH0) to 1168 kPa (G-LDH3). It was shown that the printed nanocomposite hydrogel scaffolds were able to support encapsulated osteoblast survival, spreading, and proliferation in the absence of any osteoinductive factors taking advantage of LDHs. In addition, cells encapsulated in G-LDH3 had a larger cell spreading area and higher cell aspect ratio than those encapsulated in G-LDH0. Altogether, the results demonstrated that the developed GelMA/LDHs nanocomposite hydrogel bioink revealed a high potential for extrusion bioprinting with high structural fidelity to fabricate implantable 3D hydrogel constructs for repair of bone defects.

Extracellular vesicle-loaded hydrogels for tissue repair and regeneration

Extracellular vesicles (EVs) are a collective term for nanoscale or microscale vesicles secreted by cells that play important biological roles. Mesenchymal stem cells are a class of cells with the potential for self-healing and multidirectional differentiation. In recent years, numerous studies have shown that EVs, especially those secreted by mesenchymal stem cells, can promote the repair and regeneration of various tissues and, thus, have significant potential in regenerative medicine. However, due to the rapid clearance capacity of the circulatory system, EVs are barely able to act persistently at specific sites for repair of target tissues. Hydrogels have good biocompatibility and loose and porous structural properties that allow them to serve as EV carriers, thereby prolonging the retention in certain specific areas and slowing the release of EVs. When EVs are needed to function at specific sites, the EV-loaded hydrogels can stand as an excellent approach. In this review, we first introduce the sources, roles, and extraction and characterization methods of EVs and describe their current application status. We then review the different types of hydrogels and discuss factors influencing their abilities to carry and release EVs. We summarize several strategies for loading EVs into hydrogels and characterizing EV-loaded hydrogels. Furthermore, we discuss application strategies for EV-loaded hydrogels and review their specific applications in tissue regeneration and repair. This article concludes with a summary of the current state of research on EV-loaded hydrogels and an outlook on future research directions, which we hope will provide promising ideas for researchers.

Three-Dimensional Bio-Printed Cardiac Patch for Sustained Delivery of Extracellular Vesicles from the Interface

Cardiac tissue engineering has emerged as a promising strategy to treat infarcted cardiac tissues by replacing the injured region with an ex vivo fabricated functional cardiac patch. Nevertheless, integration of the transplanted patch with the host tissue is still a burden, limiting its clinical application. Here, a bi-functional, 3D bio-printed cardiac patch (CP) design is proposed, composed of a cell-laden compartment at its core and an extracellular vesicle (EV)-laden compartment at its shell for better integration of the CP with the host tissue. Alginate-based bioink solutions were developed for each compartment and characterized rheologically, examined for printability and their effect on residing cells or EVs. The resulting 3D bio-printed CP was examined for its mechanical stiffness, showing an elastic modulus between 4-5 kPa at day 1 post-printing, suitable for transplantation. Affinity binding of EVs to alginate sulfate (AlgS) was validated, exhibiting dissociation constant values similar to those of EVs with heparin. The incorporation of AlgS-EVs complexes within the shell bioink sustained EV release from the CP, with 88% cumulative release compared with 92% without AlgS by day 4. AlgS also prolonged the release profile by an additional 2 days, lasting 11 days overall. This CP design comprises great potential at promoting more efficient patch assimilation with the host.

Hybrid extracellular vesicles-liposome incorporated advanced bioink to deliver microRNA

In additive manufacturing, bioink formulations govern strategies to engineer 3D living tissues that mimic the complex architectures and functions of native tissues for successful tissue regeneration. Conventional 3D-printed tissues are limited in their ability to alter the fate of laden cells. Specifically, the efficient delivery of gene expression regulators (i.e. microRNAs (miRNAs)) to cells in bioprinted tissues has remained largely elusive. In this study, we explored the inclusion of extracellular vesicles (EVs), naturally occurring nanovesicles (NVs), into bioinks to resolve this challenge. EVs show excellent biocompatibility, rapid endocytosis, and low immunogenicity, which lead to the efficient delivery of miRNAs without measurable cytotoxicity. EVs were fused with liposomes to prolong and control their release by altering their physical interaction with the bioink. Hybrid EVs-liposome (hEL) NVs were embedded in gelatin-based hydrogels to create bioinks that could efficiently encapsulate and deliver miRNAs at the target site in a controlled and sustained manner. The regulation of cells' gene expression in a 3D bioprinted matrix was achieved using the hELs-laden bioink as a precursor for excellent shape fidelity and high cell viability constructs. Novel regulatory factors-loaded bioinks will expedite the translation of new bioprinting applications in the tissue engineering field.

Three-Dimensional-Cultured MSC-Derived Exosome-Hydrogel Hybrid Microneedle Array Patch for Spinal Cord Repair

Exosomes derived from mesenchymal stem cells (MSCs) have been proven to exhibit great potentials in spinal cord injury (SCI) therapy. However, conventional two-dimensional (2D) culture will inevitably lead to the loss of stemness of MSCs, which substantially limits the therapeutic potency of MSCs exosomes (2D-Exo). Exosomes derived from three-dimensional culture (3D-Exo) possess higher therapeutic efficiency which have wide applications in spinal cord therapy. Typically, conventional exosome therapy that relies on local repeated injection results in secondary injury and low efficiency. It is urgent to develop a more reliable, convenient, and effective exosome delivery method to achieve constant in situ exosomes release. Herein, we proposed a controlled 3D-exohydrogel hybrid microneedle array patch to achieve SCI repair in situ. Our studies suggested that MSCs with 3D-culturing could maintain their stemness, and consequently, 3D-Exo effectively reduced SCI-induced inflammation and glial scarring. Thus, it is a promising therapeutic strategy for the treatment of SCI.